Fullerene and carbon nanotube which have a closed-shell structure and which are composed of carbon atoms alone are, owing to their novel structure, expected to be usable in the wide range of technical field such as medicine, internal diagnosis, cosmetics, etc.
Fullerene is, however, water-insoluble, and, therefore, there has been a certain limitation on the use of fullerene in these technical fields. Thus, with a view to solubilizing fullerene, there have been provided various kinds of fullerol wherein hydroxyl group is introduced into carbon atoms of fullerene (e.g., Japanese Patent Application Laid-Open Publication No. Hei 7-048302). In the case of metal-encapsulating fullerene, there have also been presented those whose surface is covered with polysaccharides having a functional group selected from the group consisting of sulfone group, ketone group, amino group and alkyl group (e.g., Japanese Patent Application Laid-Open Publication No. Hei 7-048302).
Furthermore, it has been reported that, when fullerene is added to an aqueous solution of fluoroalkyl chain-terminated acryloylmorpholine oligomer or N,N-dimethylacrylamide oligomer or the like with sufficient stirring, there are given self-organized materials (self-assembly) wherein the amount of solubilized fullerene is 100 μg/ml (see Journal of Colloid and Interface Science, 263, (2003), 1-3). It is further known that a charge transfer complex which has been prepared with use of the electron acceptability of fullerene (e.g., fullerene C60) or a C60-containing polymer which has been prepared by grafting fullerene with hydrophilic polymer such as poly(ethylene glycol), poly(vinyl pyrrolidone) and poly[(dimethylamino)ethyl-methacrylate] gives a solubilized fullerene. Moreover, C60-b-poly[(dimethylamino)ethylmethacrylate] has been provided, and its physical properties have been studied (Dai et al., Langmuir 2004, PAGE EST: 6. 8 A-G). It is suggested that this block polymer forms in an aqueous solvent a micelle having fullerene as a core and polymer as a shell, and is thus solubilized.